ABSTRACT
The effects of variously substituted quinoxalines, benzimidazoles, and benzotriazoles on Rana pipiens embryos of 2-cell (S. 3), blastula (S. 8), neurula (S. 14) and tail-bud stage (S. 18) were studied. It was found that:
Toxicity is variably increased by double substitution with two nitro groups (diN) or a nitro group and a chlorine atom (N+Cl). The relative toxicity of the single N-substituent is diminished by the addition of a hydroxy group, and generally also by a methoxy group, but not by addition of a methyl group; still greater is the diminishing effect of the carboxyl group which nullifies all activity. Cl-substitution in place of N is less toxic except at stages 3 and 8 with benzimidazoles.
Susceptibility to benzo triazoles increases with age of embryo from 2-cell to tail-bud stage 18, while the reverse is true for quinoxalines and benzimidazoles. The diN-or N+Cl-substituted compounds are exceptions, as they are highly toxic at all developmental stages under the experimental conditions.
In young tadpoles (S. 25) N-substitution increases the toxicity of quinoxaline or benzimidazole approximately 10 times, and of benzotriazole as much as 40 times.
